1. Field of the Invention
This invention relates to an integrated controls assembly and, more specifically, to control assemblies for controlling the flow of refrigerant in heat pumps and air conditioners.
2. Description of the Prior Art
The use of heat pumps to alternately provide a heating or cooling effect to an enclosed space is well-known. Such systems exhibit several advantages over conventional refrigerating or air conditioning systems which provide a cooling effect only. Reference to the theory behind the operation of a refrigerating system or air conditioner is helpful to properly emphasize the special requirements of heat pumps.
In general, a typical air conditioning system includes an inside heat exchange coil (evaporator) connected to the suction inlet of a compressor. The discharge outlet of the compressor communicates with an outside heat exchange coil (condenser) which is, in turn, connected to the inside coil. An expansion device, such as a valve or turbine, is interposed in the line between the condenser and evaporator. A suitable refrigerant is circulated through the system by the compressor.
Relatively hot, high-pressure gaseous refrigerant flows from the compressor to the condenser, where the refrigerant gives up heat to the environment and is partially condensed. The relatively high-pressure liquid or partially condensed refrigerant then flows through the expansion device where the pressure and temperature of the refrigerant is reduced. As the refrigerant flows through the evaporator, it removes heat from the surroundings by evaporation of the condensed refrigerant. From the evaporator, the predominantly gaseous refrigerant flows to the compressor to complete the cycle.
In a heat pump system, the flow of refrigerant may be reversed when it is desired to switch the system from a cooling mode to a heating mode, or vice versa. In such a system, the functions of the inside and outside coils are reversed. Therefore, several additional components are required.
A reversing valve must be provided in the heat pump system to change the direction of flow of discharged refrigerant to the inside coil rather than to the outside coil when changing the heat pump's operation from the cooling mode to the heating mode. Reversing valves require four plumbing connections.
A suction line accumulator is typically interposed in the line leading from the evaporator to the suction inlet of the compressor, and requires two plumbing connections. The function of the accumulator is to trap liquid refrigerant which has failed to be evaporated and to prevent that liquid from entering the compressor. It is often desirable to provide a re-evaporator within the accumulator in order to allow the trapped liquid refrigerant to evaporate and return to the compressor suction inlet. An additional requirement of the accumulator is to allow the return of trapped lubricating oil and other unvaporizable liquids to the compressor at all system flow rates.
Heat pumps require a capability for defrosting the evaporator, especially when the heat pump is operating in its heating cycle. During the heating cycle, the outside coil acts as an evaporator, thereby removing heat from the area surrounding the coil. Thus, the evaporating temperature may fall below 32.degree. F., thereby causing water vapor in the surrounding environment to condense and crystallize on the exterior surfaces of the evaporator's coil. Such crystallization is undesirable, as the resulting frost hinders efficient heat transfer. A known method of removing the frost is to direct hot gas from the compressor discharge to the outside coil for a period of time sufficiently long to melt the accumulated ice. This reversal of flow temporarily halts the release of heat by the inside coil, and therefore requires a supply of heat from another source, such as a resistance heater, for example.
A heater for the compressor crankcase is usually provided in heat pumps to maintain the crankcase oil at a temperature higher than the refrigerant in other parts of the system. This is desirable in order to reduce the migration of refrigerant to the crankcase. As a result, oil foaming at startup is reduced and oil loss and bearing wear problems are reduced.
For examples of typical heat pump operation and construction, attention is directed to U.S. Pat. Nos. 3,651,657 (Bottum), 3,412,574 (Reiter), 3,381,487 (Harnish) and 3,012,414 (LaPorte).
Previous systems including the above-described features presented problems related to cost and efficiency of operation. The cost of multiple safeguards, as described above, tends to be relatively high. This cost is compounded by resulting size requirements, as multiple components occupy a relatively great amount of space. Efficiency was hampered by relatively great external power requirements associated with the reversing valve and crankcase heater, and by the periodic interruption of operation for the purpose of defrosting the evaporator.